An example of a conventional storage device including discs confirming to Serial Attached SCSI (SAS) is a Redundant Arrays of Inexpensive Disks (RAID) system. Supporting a large number of discs included in the system, some storage devices each include a Controller Enclosure (hereinafter called CE) playing as a principal role in the system and a number of Drive Enclosures (hereinafter called “DE”) accommodating a number of additional discs.
Since the SAS does not permit coupling in a loop shape, each controller module (hereinafter called CM) of the CE (hereinafter CE-CM) and a CM of a DE (hereinafter DE-CM) and a number of DE-CMs need to be serially coupled to one another in the order of adding the DEs so as to form a daisy chain (hereinafter called serial coupling) as illustrated in FIG. 19. However, in the event of a failure occurring in one of the DE-CMs on the access route, the CE cannot access the failure DE and the DEs downstream of the failure DEs . As one of the solutions, a conventional storage device includes redundant CE-CMs and DE-CMs (e.g., two CE-CMs and two DE-CMs) and additionally, the CE and a DE, and DEs are coupled to one another via redundant (e.g., two) routes as illustrated in FIG. 20.
Alternatively for example, a known storage system physically couples a vacant port of a controller or a switching device and vacant ports of other switching devices into a loop, which are however logically regarded as two cascaded routes by logically separating the routes by a routing table. Even when a failure occurs in either route, simple variation of the status values in the routing table allows the controller to be logically coupled to switch devices through the other route free from the failure, so that the operation of the system can be continued.
[Patent Literature 1] Japanese Patent Application Laid-Open (KOKAI) Publication No. 2008-71005
[Patent Literature 2] Japanese Patent Application Laid-Open (KOKAI) Publication No. 2005-293595
However in the above storage device, in the cases where a failure occurs in one of the DEs on the access route, that is, in the cases where the redundant DE-CMs in the failure DE become inaccessible, the CE cannot access the failure DE and additionally the DEs coupled downstream of the failure DE.
Furthermore, in the storage device coupling the controller and switching devices into a loop through the use of vacant ports of the controller and switching devices, increase in the number of switching devices complicates physical path wiring, resulting in complex wiring managing.